Here in Kingston over the next week it will drop to as low as Minus- 29 deg C.
I suspect if you see similar temps you may be able to place the crossbow outside foe enough time that the cold may may cause just enough metal contraction to allow it to free up.

If nothing else works and your season is over ? Perhaps send the riser only to Danny Miller, or if living North of the Border ? back to customer service at Excal and they may be able to get them out with no damage to your riser.

All it would take is a phone call to Dawn or Danny to see if that could be a option for you.
Just a thought.

However, If it was me, having used DR bumpers with the Excal posts on one of my Micro 355's, ( that's the way they are designed to be used) I would definately forget about removing them and go that route.